Modern optical communication systems comprising optical communication paths are capable of transmitting optical traffic signals several thousands of kilometers between network elements, without any requirement to regenerate the signals. As a result, any monitoring of the traffic on the communication paths is typically performed at the input and output ports of the network elements.
The monitoring of the traffic on the communication paths is necessary in order to determine the optical signal-to-noise ratio, the power of the traffic and to generate transmission reports, for example. The monitoring points typically comprise optical splitters which are arranged to extract a portion, typically 1-10% of the optical signal from the communication path, so that the portion of traffic can be subsequently analysed. The analysis may comprise passing the traffic to a photodiode for measuring the optical power on the path to control the power on the path for example, or to an optical spectrum analyzer for a subsequent analysis of the frequency components of the traffic.
When monitoring the optical power of the traffic on the path, since only a total power is presented to an operator for example, then no useful traffic information can be deduced. However, since the individual traffic components are exposed with a spectrum analyzer, then this presents a security issue, since the traffic content on the path can be monitored. Any network element having a monitoring port through which the network traffic can be accessed is thus vulnerable to eavesdropping. This is particularly true for unattended network elements such as optical amplification sites, deployed at remote locations.